Abstract: The structure of the vacuum system of the pre-beam line of HIRFL is introduced.The conductance,the outgassing and the pressure gradient before upgrade are given in detail. A concrete upgrade outline is made out.The expected pressure has been obtained and kept:the working pressure of a pump is lower than 5×10^-6Pa,the working pressure of the center between two pumps is not more than 1×10^-5Pa.It means that the upgrade of the vacuum system of the pre-beam line of HIRFL is feasible.